Can we modify built-in object prototypes in JavaScript

JavascriptWeb DevelopmentObject Oriented Programming

Following is the code for modifying built-in object prototypes in JavaScript −


 Live Demo

<!DOCTYPE html>
<html lang="en">
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
   body {
      font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
   .result {
      font-size: 20px;
      font-weight: 500;
      color: blueviolet;
<h1>Modify built-in object prototypes</h1>
<div class="result"></div>
<br />
<button class="Btn">Click Here</button>
<h3>Click on the above button to call the alert method</h3>
   let resEle = document.querySelector(".result");
   let BtnEle = document.querySelector(".Btn");
   window.alert = function (msg) {
      resEle.innerHTML = "Custom Alert function has been triggered<br>";
      resEle.innerHTML += "Alert Message = " + msg;
   BtnEle.addEventListener("click", () => {
      alert("Hello World");


On clicking the ‘Click Here’ button −

Updated on 18-Jul-2020 07:56:14